Carrier adapter circuit



P. BAKKER CARRIER ADAPTER CIRCUIT July 8, 1958 '3 Sheets-Sheet 1 Filed March 24, 1955 w m mm.

mm A 7 B R Y B v1 ATTY.

July 8, 1958 P. BAKKER CARRIER ADAPTER CIRCUIT 5 Sheets-Sheet 2 Filed March %4, 1955 N Q'Y 4v. c5 03 t6 2252.55 *9;

HVVENTUR. PIER BAKKER ATTYI y 1953 P. BAKKER 2,842,622

' CARRIER ADAPTER CIRCUIT Filed March 24, 1955 3 Sheet Shee-t 3 8n won; L4

INVENTOR. PIER BAKKER BY I fl ATTY.

8m tG 2922515 SEQ 3528 no;

United States 2,842,622 CARRIER ADAPTER crnctur Pier Bakker, Chicago, 111;, assignor to General Telephone Laboratories, Incorporated, a corporation of Delaware Application March 24, 1955, Serial No. 496,553

13 Claims. (Cl. 179--43) The practice in the telephone art is to terminate each inter-ofiice trunk in a line which may be seized from a selector level if automatic service is provided between exchanges and directly by an operator if manual service is provided. At the incoming office an incoming selector is connected to the line or trunk and it is operated over i a dialling loop immediately completed thereto on seizure of the trunk at the outgoing office, or if the incoming office is a manual ofiic'e an operator is signalled. A trunk circuit for use in an arrangement of the type described is usually dry, when idle, that is without current flowing therein due to no battery or ground being connected thereto or it may have ground connected to ground and battery connected to battery at the respective stations over respective sides of the trunk. On seizure the line is supplied with proper potentials to operate the equipment at the incoming oifice to signal that ofiice and seize the incoming selector thereat. To meet these conditions and variations thereof many well-known carrier adapter circuits have been devised to enable carrier transmission systerns to be used with the exchange equipment without disturbing the standard battery and ground connections at the trunk terminations.

However, a private branch exchange or ofiice, commonly known as a P. A. B. X, is usually accessible to a central ofiice connector switch through a line circuit individual to the P. A. B. X in the same manner as an ordinary subscriber, and likewise if automatic service is provided to the P. A. B. X, a P. A. BLX subscriber has access to a called subscriber by means of the central office switching equipment controlled through the line circuit. If the P. A. B. X were accessible from a selector, an entire level of each selector bank would be rendered inaccessible to other calls regardless of the number of the trunks between the central cities and P. A. B. X, and therefore it has been found most economical to have the P. A. B. X accessible to a connector switch on an in coming call to the P. A. B. X. The line circuit through which the connector has access to the P. A. B. X may be used to associate the central office switching equipment therewith on an outgoing call from the P. A. B. X. The line circuit may be easily converted to signal the P. A. B. X immediately when it is seized in the central ofiic-e to prevent those on the verge of calling from the P. A. B. X from using the line. Regular subscribers lines normally have ground connected to one side of the line and battery to the other. P. A. B. X trunks however, when terminated in a line circuit in the same exchange, must. have this ground to the one side of the line normal- 1y disconnected. Disconnecting ground from the positive side of the line by slipping an insulating sleeve between the springs at the line circuit connecting ground to the positive side of the line provides an economical conatent number.

version of an ordinary subscribers line circuit to a P. A. B. X line circuit. The negative side of the line is maintained connected to battery through the line circuit line relay. When the line circuit is arranged as above, equipment may be bridged across the line at the P. A. B. X without being operated except when the central office connector switch or an operator disconnects the line relay and applies ground and battery to the line, when seizing it at the central office. Operating the bridged equipment at the P. A. B. X busies the trunk circuit at the P. A. B. X to prevent someone at the P. A. B. X from seizing the trunk circuit while the connector switch is applying ringing current to the trunk and thereby receiving a very unpleasant sensation or interfering with the call. Likewise the P. A. B. X termination of the trunk is usually provided with an open positive line to maintain the line circuit line relay at the central office and the bridged equipment at the P. A. B. X normally unoperated while permitting the line relay at the central oilice normally connected to battery to be operated on a call from the P. A. B. X after disconnecting the bridge equipment at the P. A. B. X and closing one side of the line to ground in the P. A. B. X. Operation of the line relay immediately busies the central ofiice termination to outgoing calls therefrom. From the foregoing description it will be appreciated that a dialling loop is not complated on a call to the P. A. B. X and is completed on a call from the P. A. B. X only after the operated line relay in the central oifice causes certain central ofiice switching equipment to be associated with the line circuit and return ground and battery back over the trunk so that a call may be automatically extended. Of course if the central ofiice is manual the operated line relay signals the operator and she completes the call to a desired central r ofiice subscriber.

It will be understood that one or more repeating coils may often be provided between the P. A. B. X and the central ofiice so that the circuits terminating in either office may not be physically connected together and that various arrangements are adopted to repeat signals around the coils.

From the foregoing description it maybe readily appreciated that a number of diflferences exist between the ordinary inter-exchange trun'ks wherein standard carrier transmission systems are most generally used and for which carrier has been primarily designed and the P. A. B. X circuits of the type described, and that the accomplishment of various signalling requirements by means of the P. A. B. X circuits described proceeds in a manner different than in ordinary inter-exchange trunks necessitating numerous and diificult adaptions before a standard carrier transmission system can be used with P. A. X circuits of the type described.

It is therefore an object of the present invention to provide an arrangement utilizing a standard carrier transmission system between ofiices which have an open positive line associated with those circuits which are available for use in extending a call such as the P. A. B. X trunks above described, and it is a further object of the present invention to enable such circuits to provide conventional signalling results in response to dial pulses and other signals transmitted over the carrier equipment.

The invention is described herein as operating in conjunction with a P. A. B. X and a central office which may be either an automatic or manual type oilice. The circuits are arranged so that either a P. A. B. X subscriber or attendant can connect directly to the central cifice via the carrier transmission equipment and if the central ofiice is arranged as an automatic type, a call is automatically completed directly to a subscriber in the central oflice on the dialling of the called subscribers if the central ofiice is arran ed as a manual ofdesigned to provide interrupted ringing current.

fice of course the operator thereat is signalled to answer the call and she completes the call. incoming calls to the P. A. B. X are completed from a subscriber in an automatic central oiiice directly to the P. A. B. X attendant, who after receiving a calling signal and answer ing the call connects to the P. A. B. X subscriber. the central oiiice is a manual one the operator therea; completes the call to the attendant at the P. A. B. X and she connects the desired B. X subscriber.

addition it will be noted at this time that provision if} made for a central ofiice operator to signal the P. A. B. X attendant as often as desired during the period in which a connection is already established.

Figs. 1 and 2 respectively illustrate an ordinary type of P. A. B. X trunk circuit Iiiltl and a P. A. B. X termination circuit 209 adapted to enable the trunk circuit iilil to operate with carrier equipment. These circuits are accessible to an attendant through jack i lor to P. A. B. X subscriber such as S2 over switch train when making an outgoing call. Fig. 2 also includes block 2G1 for indicating the carrier equipment at the P. A. B. X office which is utilized with the aforementioned circuits for extending calls between the P. A. B. X and the central ofiice over line 2%.

Fig. 3 illustrates the central ofiice termination circuit friltl accessible from the P. A. B. X on a call to the central ofiice over the line 2&2 and the carrier equipment indicated by the block Still. It has connected thereto over the +1. and L conductors, a conventional line circuit (not shown) of the type wherein ground is disconnected from the +1. conductor as previously explained. As already mentioned the central omce may be either of a manual or automatic type, and if the latter a subscriber in the central ofiice has direct access to circuit 3% for connecting to the P. A. B. X circuits and he is accessible directly from circuit 390 over the central office switching equipment on a call from the P. A. B. X.

A switch train 3 comprising any well-known type of finder and selector switches of the battery searching type is available to a P. A. B. X subscriber for extending a call. He may extend the call to a trunk circuit such as trunk circuit Mill and P. A. B. X termination circuit 2% having access to the central office circuits over carrier equipment Ztil and 331 by dialling a predetermined digit on the selector switch. The selector switch on finding trunk circuit Hi0 idle in turn switches through in any well-known manner to operate relay ill. Relay llllinitiates a series of operations for closing ground to the +T conductor leading to the P. A. B. X termination circuit 2% by means of relayv 22!} to complete the seizure of that circuit. it also busics the trunk circuit Wt) to incoming calls from another switch train such as 5 and to the P. A. B. X attendants. if the central orfice is of an automatic type it is provided with switching equipment or" any well-known type whereby a connection may be established over a switch train of the type described from a central oriice subscriber to circuit 3% or on L in from circuit 3% to a central ofice subscriber, that train including a connector switch ot-any well-known type it will also be understood that such switches are provided with means for 'eturning ground and battery over the +L and L conductors respectively when associated with circuit Silt? and that the connector switch is provided with well-known ring cut-off and reverse battery rela s.

Relays Silt 22a in P. A. E. X termination circuit 194 are operated on seizure. Relay 22% actually closes ground-to the +3 conductor to complete a loop circuit for relay are which is already operated. Relay are forwards battery over the signal-out lead S0 to cause carrie equipment Ztll to forward a tone of a particular frequency over line to carrier equipment which contains any well-known type of control equipment operated in response to the received particular tone frequency to apply ground to the signal-in lead SI and operate relay 31 3 in the central olfice termination circuit 3%.

The carrier equipment is of any well-known type such as the Lenkurt type 45A constructed to transmit a tone signal on the application of battery to the respective signal-out leads S0 or S0 at the respective stations and arranged to rectify the transmitted tone and provide a 3,-C lil'ld to the respective signal-in leads SI or S1 at the respective stations. Voice frequencies are transmitted over one portion of an available band width and the tone frequencies emanating from the respective stations are transmitted as respective sidebands over another portion of the available band width in any well-known manner. it will be appreciated that any number of different arrangements may be utilized in place of that described and although a physical line 262 is shown connecting carrier equipment 2491i and 301, it will be understood that the line may be dispensed with, if the carrier equipment incorpora'es radio transmission.

Relay 31% operates to operate relay 320 which in turn operates relay 37% and relay 370 in turn operates relay et}. The line circuit (not shown) associated with circuit 3% is of any well-known type which provides battery through a line relay (not shown) to the -L conductor but no ground for the +L conductor as previously mentioned. The upper and lower windings of high resistance relay 339 are normally connected between battery on the L conductor and the +L conductor. It is disconnected on operation of relay 320. Relay 32 connects ground through relay 370 to battery on the L conductor through the line relay and both are operated. Operation of the line relay initiates operation of the automatic switching equipment in the exchange and busies the line circuit to calls from the central oifice in any well-known manner. The automatic switching equipment in the exchange comprises any well-known type of finder, selector and connector switches, each of which is arranged to send ground back over the +L conductor and battery over the -L conductor through their re spective line relays. Thus when the line circuit associated with circuit 360 is found by the appropriate switch, ground is sent back over the +L conductor and battery over the L conductor and the line circuit cut-off relay (not shown) is operated in any well-known manner to disconnect the line circuit line relay. The ground on the +L conductor is sent over a circuit prepared by relay 37-9 to operate relay 360 which in turn completes the loop from the line relay over the +L and -L conductors through relay 37d and removes the original operating ground from relay 370.

if the exchange is a manual one an operator must co l.- plete the connection. "i" he same series of operations takes place for disconnecting relay 334 and connecting relay 379 so that the line relay can operate and signal an operator. The operator then completes the connection.

On calls to an automatic exchange the P. A. B. X subscriber operates his dial in any well-known manner to pulse relay 10. The pulses are repeated at contacts ii to pulse relay 21% over its loop circuit. Relay 2 3.9 in turn pulses the carrier relays which in turn pulse relay 314 in any well-known manner. Relay 310 pulses the automatic switching equipment at contacts 313 to operate the equipment to the desired position. On completion of the connection the called subscriber is automatically signalled by interrupted ringing current applied to his line in any well-known manner. On answer a t lking circuit is-ccmpleted over the loops extending over switch train 3 and repeating coils 99, 2.99 and 3% and the loop extending over the automatic switching equipment to; the called subscriber.

The P. A. B. X attendant extends a connection to the central office in a similar. manner using her cord circuit and jack 14. Likewise if an operator in the central ofiice must extend the connection she utilizes her cord circuit for first completing the talking circuit to the P. A. B. X attendant and then to the called subscriber. The cord circuits are of any well-known type which include equipment for controlling automatic equipment and for completing talking circuits over the same repeating coils as described above.

On an incoming call to the P. A. B. X the central oflice termination circuit 303 is seized first in any well-known manner from a connector switch in the central ofiice or by an operator pluggingin to seize the circuit. Ground and battery are extended over the +L and -L conductors respectively. As relay 330 is in the loop it operates. Relay 340 operates under control of relay 330 to apply battery to lead SO and cause a tone signal to be transmitted over carrier equipment 301 and 201 and ground to be placed on lead S1 to operate relay 270. Relay 27d operates relay 23% and it in turn applies ground to the +T conductor. High resistance relay 90 in trunk circuit m0 is operated thereby to seize the trunk circuit and busy it to calls from the P. A. B. X.

When the connector applies interrupted ringing current over the }-L and L conductors or the operator manipulates her ringing key, A. C. relay 380 in circuit 300 is operated and released. Relay 270 releases when relay i 384) is released and then it is reoperated. Relay 270 releasing and reoperating gives rise to a cyclic operation for relays Mil, 25d and 268 to apply A. C. ringing current to the +1? and T' conductors for operating A. C. relay 95. Relay 95 operates the P. A. B. X attendants calling lamp so that an attendant answers the call. The P. A. B. X attendant signalling operation proceeds as long as interrupted ringing current is applied to relay 380.

When the P. A. B. X attendant answers relay it) is operated to complete a loop circuit for operating relay 216. Relay 21d applies battery to lead SO to operate relay 31d in circuit Relay 310 shunts the high resistance lower winding of relay 330 from the loop circuit at contacts 35.3 to allow the connector ring cut-off relay and the reverse battery relay in the connector to operate and cut oil the interrupted ringing current and provide answer supervision for the calling party respectively. Likewise the short circuit of the lower winding of relay 330 enables a relay to operate and signal the operator that the call is answered in the case of an operator completed call. The P. A. B. X attendant completes a talking circuit to the calling position and then connects the desired P. A. B. X subscriber to the calling position and completes a talking ciruit therebetween. Also if the connection to the P. A. B. X is from a manual ofiice, the operator thereat may again manipulate her ringing key to repeat the operation for releasing relay 270, reoperating it and reoperating relays 24 6, 250, Edit and A. C. relay 95 to again signal the attendant. The attendant may then complete a connection to another P. A. B. X subscriber. A more detm'led and comprehensive description including the respective release operations is described in the following sections enn'tied outgoing P. A. B. X calls and incoming calls respectively.

Outgoing P. A. B. X calls A P. A. B. X subscriber such as S2 initiates a call to a subscriber in the main exchange and by dialling a predetermined digit overswit h train 3 steps the battery searching selector switch of the train to a level corresponding to the digit, where it automatically hunts for an idle trunk circuit such as trunk circuit 100. In hunting for an idle trunk circuit the selector switch tests trunk circuit lull by searching for battery over lead C, contacts. 8 associated with each attendants jack individualto the trunk, contacts 35 and the lower winding of relay 30. This is only a resistance winding so relay 3% does not operate from ground placed on the C lead at the selector. On finding battery the selector terminates its hunting operation, and the switch through relay therein operates to complete a loop circuit to relay it) from battery through the lower winding of relay It the lower left winding of repeating coil 99, contacts 63, the lead to the switch train loop, over the switch train loop including the dial springs of the calling subscriber and back over the lead, through the upper left winding of repeating coil 99 to ground through the upper winding of relay 10.

Relay 10 operates and closes contacts 12 to complete a circuit to slow-to-release relay 2%, and at contacts 11 it completes a circuit including ground at contacts 51, the upper right winding of repeating coil 99, the winding of relay 40, the lower right winding of repeating coil 99, the -T' conductor to the P. A. B. X termination circuit 200 and over contacts 254, the lower left winding of repeating coil 2%? to battery through the lower winding of relay Elli. Relays to and 210 operate and the results thereof will be described shortly.

Relay operates to close contacts 21, and 24 and opens contacts 22 and 25. Contacts 2i prepare a point in a loop circuit through the P. A. B. X attendants cord circuit which will not be used on this type of call. Contacts 23 prepare a circuit to relay 70, and contacts 24 complete an obvious circuit through the upper Winding of relay 30. Contacts 22 are opened to open a point in the P. A. B. X answer lamp circuits while opening contacts 25 opens a point in a circuit for operating relay Elli. Relay now operates, and opens contacts to remove battery from lead C, while at contacts 32 it grounds lead C so as to busy trunk circuit 100 to incoming calls from other P. A. B. X subscribers and hold the selector switch in train 3. At contacts 34 it completes the circuit to light the busy lamps such as 4 individual to trunk circuit ltill at all appropriate P. A. X attendant positions so that they do not attempt to utilize this trunk circuit.

Relay 4!! as previously described is operated by relay 19, and it closes contacts 41 to prepare a circuit to slowto-release relay 50. The circuit to relay 5% is completed when relay 210 closes contacts 211 to energize slow-torelease relay 220, which in turn closes contacts 212i to forward ground through the upper winding of relay 2M), over contacts 251, the +T' conductor and contacts 55 and 41 to relay 50. Relay 50 operates to complete a holding circuit for itself over contacts 53 and 41, while simultaneously opening its original operating circuit at contacts At contacts 51 it opens the original operating circuit for relays and 210, but at contacts 52 it completes a new circuit for relays 40 and 210 from ground at contacts 221 forwarded over the +T conductor, contacts 52 and already described portion of the operating circuit for relays 40 and 210. Relay also closes contacts 54 to complete an obvious holding circuit for the upper winding of relay 30.

Relay 210 on operating also closed contacts 212 to cause battery to be forwarded over the low resistance winding of relay 270, contacts 212 and the signal-out lead S0 to operate the signal-out relay (not shown) in the carrier equipment 201. Because of the low resistance winding, relay 270 does not now operate. The signalout relay and the carrier equipment now cause a tone of a particular frequency to be sent out in any well-known manner from the carrier equipment 2M over the line 2%2 to the carrier equipment 301 in the central ofiice. A signal-in relay (not shown) in carrier equipment 301 open ates in response to the received particular frequency to ground the signal-in lead SI and operate relay 31th, which in turn operates relay 320.

if the central ofiice termination circuit Silt) terminating carrier equipment 301 has direct access to automatic equipment for enabling the calling party to connect directly to a called party a loop circuit is normally prepared from battery through the winding of a line relay o w in the i e r uit ssociated with. circuit Relay out, is disconnected from the aforementioned p.

' pared loop by relay 329 and ground is connected through relay 37d to the L conductor in a manner to be described so that the line relay operates to initiate operation of the automatic equipment or it circuit 3% is accessible to an operator, the operators jacl; rt ates to signal her.

Relay 316i closes contacts 332 to complete a circuit to slow-to-release relay 32% from ground at contacts 3 3i. and it also closes contacts 313 to prepare a circuit for relay are and the line relay. Slow-to-release relay 3Z9 operates to close contacts 321, 322, 323, 32 iand 325 and open contacts and Contacts 31.27 open to disconnect the aforementioned prepared loop circuit through unoperatcd relay 3%. Condenser 397 and resister 397 which provide a load circuit for the carrier equipment when the equipment is idle, are disconnected at contacts A; com. ts and the prepared circuit for relay 3-76 and the line relay is completed from ground at contacts through relay 3%, the lower right winding of repeating coil 39%, contacts 346, 313 and 325, the L conductor, to battery through the line relay. Relay 379 operates and prepares a circuit for relay 360 at contacts 371.

The relay operates in series with relay 374 over the aforedescribed circuit and it initiates operation of the automatic equipment. When the equipment is prepared to receive dial impulses ground and battery are returned over the +L and L conductors respectively from the line relay (not shown) in the first selector switch of the automatic equipment and the originally operated line relay of the line circuit is disconnected all in a well-lznown manner. Ground from the +L conductor is forwarded over contacts 361 and 777i to energize the lower winding of relay 36%? which operates to prepare a holding circuit for its lower winding at contacts At contacts 361 it opens its original operating circuit and closes a new one from ground at contacts as: forwarded over contacts 317?. The operating circuit for relay 37% is opened at contacts 365 and a new circuit therefor completed from ground on the }L conductor, the upper left Winding of repeating coil 399, contacts 366 and the already described portion of its operating circuit to battery on the L conductor. At contacts another point in the carrier equipment idle terminating load circuit comprising resister 397' and condenser 397 is opened.

If an operator must eXtend the call a line or jack relay is operated in series with relay 3: ll over a circuit similar to that already described for controlling a signal at the operators position. The operator on being signalled plu s her cord circuit in to provide ground and battery to the +L and -L conductors respectively thereby giving rise to the already described sequence for maintaining relay 37 operated and for operating relay in the meantime operated slow-to-release relay 329 closed contacts 321 to forward battery over contacts 361' and the signal-out lead S to operate the signal-out relay (not shown) or" carrier equipment 301. The signa1-out relay of carrier equipment 301 on operation causes an appropriate tone signal to be sent over line 2% to the signal-in relay (not shown) of carrier equipment 2% which now applies ground over the signal-in lead SI through the upper winding of relay 270 to operate relay 27h. Relay 270 closes contacts 271 to operate slow-torelease relay 230, which in turn closes contacts 231- prepare an alternate holding ground for the upper winding of relay 210 and opens contacts 232. Condenser 298 and resistance 297 which provide a load circuit for the carrier equipment, when the equipment is idle, to prevent the equipment from Whistling or oscillating are disconnected by the opening of contacts 232 as the other elements of the circuit now provide the load. The ringing machine is started at contacts 235, however as contacts 275 remain open as long as relay 270 is operated, relay 3 cannot be operated to operate relay 250, which would send the ringing current back over the +T and -"l"' conductors to signal a P. A. B. X attendant.

If the called subscriber is in a manual otfice the operator on inserting the plug of her cord circuit in the jaci; at her position terminating circuit 3% may converse with the calling party over a talking loop including the and leads in Fig. l and contacts 63, the left wind ings of repeating coil 9 and condenser 9 the right windings of repeating coil 99 including condenser shunting talking current from relay 49, contacts 11 and 52;, +1" and -T' conductors, contacts 251 and 25 4, respectively, the left windings of repeating coil 2% and the condenser between its winding, the right windings of coil Z99, carrier equipment 201, line 3&2, carrier equipment Sill, the left windings of coil 3&9, and a loop circuit from the operators cord circuit including the +L conductor, the upper right winding of coil 3%9, condenser 3% shunting talking current from relay 370, the lower right ing of coil 399, contacts 346, 313 and 325' and tire -L conductor to the operators cord circuit. On securing the desired information the operator at the manual exchange proceeds to extend the call in any well-known manner and complete it over her cord circuit. It will be remembored that the tone signal remains on the respective signalling leads but is prevented from interfering with the talking circuit by appropriate filtering elements in the carrier equipment.

On the other hand, if the call is to an automatic otlice the P. A. B. X subscriber must extend the call over the automatic equipment to the called subscriber by dialling the called subscribers number. Dialling of the called subscribers number over the and leads from switch train 3 causes relay 1% to follow the dial pulses in any well-known manner and open contacts 11 accordingly. Opening of contacts 12 has no efiect on relay 2% as it is sloW-to-release, and therefore it remains operated during the dialling of each digit. Each time relay it} releases it closes contacts 13 to complete a circuit over contacts 11 and 69 to operate sloW-to-release relay 7%). Relay opens contacts 71 to remove relay from across talking circuit, closes contacts 74 to complete al holding circuit for relay 5G, and at contacts the impulses repeated at contacts 11 around coil 9,, relay 4d and condenser 49 via the resistance 6. Condenser 3"? and resistor 38 are provided for spark suppression. Relay 4t) releases when contacts 11 open, and it ope s the original holding circuit for relay 5% however 1' being slow-to-release remains operated until relay 7G operates to complete the additional holding circuit scribed for relay 50. Relay 50 therefore does not restore while the digits are dialled.

Relay Z10 releases on each pulse as its circuit is opened at contacts 11 and it follows the dial pulses to pulse co. tacts 212 accordingly. Condenser 215 and resistor in are provided to suppress sparking at contacts .12. The signal-out relay of carrier equipment 281 is thereby a pulsed accordingly to operate the signal-in relay of cc 1 equipment 391 accordingly. This causes the relay 3119 connected to lead SI to be pulsed in accordance with the dialled digits. Relay 310 pulses the line relay of the appropriate switches of the automatic switching equipment at contacts 313 over a circuit to be described to cause the switch train to be operated to connect to the called party. Condenser 314 and resistor 315 provide spark suppression for contacts 313. Relay 320 does not release during the periods of relay 310 as it is slow-torelease. Slow-to-release relay 350 is operated on the first release of relay 31$) over contacts 341, 311 and 322 and remains operated while each digit is dialled. The upper winding of relay 366 is also energized over a circuit including the same contacts. This is done to insure relay 36h remains energized during each series of digits as it has a heavy spring load. A holding circuit for the lower winding of relay 369 is completed from contacts 353 and 363. A shunt circuit at contacts 352, 354, resistor 375, contacts 324, 367, 346, 313 and 325 around the secondary of coil 399 and relay 370 is provided to improve pulsing to the switching equipment. Because of this shunt, relay 37h restores during each digit. It is reoperated after each digit is dialled as the shunt completed by relay 350 at contacts 354 is opened when relay 350 is restored after each digit by the opening of contacts 311. Relay 356 also closes multiple battery to the SO lead at contacts 355. Relay 370 opened the circuit to the lower winding of relay 360 at contacts 371 when it restored, but as previously explained relay 360 is held by other circuits completed to 'both its upper and lower windings. At the end of the dialling operation relay 350 is restored finally to open the holding circuit to the lower winding of relay 360, however the latter is held operated by relay 37% over its original operating circuit. The circuit to its upper winding is opened at contacts 311.

The called party is automatically lung from the connector switch of the switching equipment, and on answer by the called party a talking circuit simliar to that already described but omitting the operators cord circuit and including the loop over the switching equipment is completed between the parties. In the trunk circuit 100, relay is again continuously energized and relay 70 restored as contacts 13 remain open so that the trunk circuit is in the same condition as on seizure. Likewise, relays 210 and 310 are continuously operated to maintain circuit 2% and circuit 300 in the same condition as on seizure.

It will be understood that the called party on releasing merely causes the connector switch to restore the original polarities to the +L and -L conductors or if the connection is completed by an operator, the operator is signalled to apprise her that the called party has disconnected. The operator may remove her cord circuit, but this merely releases relay 366 for no purpose as relays 310, 370 and 320 maintain circuit 300 seized.

The P. A. B. X subscriber on disconnecting opens the loop to relay 10 and it releases to open contacts 12 and relay starts to restore. Before relay 29 restores relay '70 is operated over a circuit already described and it provides a holding circuit for relay 5% at contacts '74.

. One circuit to the upper winding of relay is opened at contacts 24, when relay 20 does restore, but relay 30 is held operated from contacts 54. In the meantime before relay 20 is restored the circuit through relays 40 and 218 is opened at contacts 11. Relay 210 releases to open the circuit to relay 220 at contacts 211, but as it is slowto-release, it maintains ground on the upper winding of relay 210 for a short period thereafter. Relay 230 controlled by relay 27% also maintains ground on the upper winding of relay 21% at contacts 231. Relay 40 opens contacts 41 to open the original holding circuit for relay 50, but it is held operated as already described. When relay 2% is finally restored to close contacts 25, ground is provided from contacts 231 or 221 as relay 220 is not yet completely released, over contacts 251, the +T' conductor through relay 9% contacts 25 and 65 to battery through the lower winding of relay 210. As relay 90 is of high resistance as compared to relay 210 it only is operated and maintains a holding ground for relay which in turn retains relay 30 operated at contacts 54. Relay 30 maintains trunk circuit 100 busy as previously described.

Relay 21% in series with relay is released and starts the restoration of relay 220 at contacts 211 while at contact 212 it causes the restoration of the carrier signal relays and the removal of ground from lead S1 to restore relay 31h. Relay 310 restores to open the circuit to relay 326 at contacts 312. It also opens the circuit to the connector switch line relay and relay 37% at contacts 313. Both release and the switching equipment also starts to release. sure of contacts 311 completes an already described circuit for operating slow-to-release relay 35d and energizing the upper winding of relay 360. Relay 35h establishes an already described holding circuit for the lower winding of relay 365 and closes the multiple from battery to lead S0 at contacts 355'. In the event the switching equipment is not completely released by the time 328 restores, the previously described prepared loop circuit excepting the upper right winding of coil 399 which is shunted at contact 352, and including relay 33% is completed to the +1. and L conductors from the line relay of the unreleased switch. It the switching equipment is completely released by the time relay 320 is restored the prepared loop circuit to relay 336) is established, but remains incomplete as ground is not provided to the +L conductor for the reasons already stated. Relay 3% is of high resistance and being in a loop circuit with the line relay of the unreleased switch, it operates, and insures the restoration of that line relay so that the switching equipment continues to release, and when released removes ground from the +L conductor. Relay 32G restores to restore its contacts and open the circuit to relay see and the upper winding of relay 360 at contacts 322. Neither is immediately restored. At contacts 321 the original battery to the SO lead is removed but as relay 35% is still operated battery at contacts 355 remains thereon until relay 35h restores at which time battery is removed from the SO lead. If relay 330 is operated by the release of relay 32% before ground is removed from the +L conductor, it operates relay 34% to maintain battery on the SO lead at contacts 343 before release of relays 350 and 360. Relay 34% opens the circuits to relay 350 and the upper winding of relay 360 but those circuits are already opened at contacts 322. Relay 340 at contacts 348 maintains the idle load circuit disconnected. Relay 350 restoring removes the shunt around the upper secondary of coil 399 at contacts 352 and opens the holding circuit for the lower winding of relay 360 and it restores. Battery is removed from the SO lead at contacts 355 however it is still applied at contacts 343. Relay 360 of course releases shortly after relay 350 to open the holding circuit to its lower winding at contacts 363 and prepares the carrier idle load circuit at contacts 368. @n complete release of the switching equipment ground is removed from the +L lead and relay 33th restores to restore relay 340. It in turn connects the idle load circuit at contacts 348 and removes battery from lead 50 at contacts 343 to cause the removal of ground on lead SI in circuit 200 to restore relay 270.

If the loop circuit is completed through an operators cord circuit relay 330 is operated, after relays 31th and 320 release, over the loop circuit to operate slow to-release relay 340 at contacts 331. Release of relay of course operates relay 350 and maintains see operated for some time after relay 326 releases. Battery is thus maintained on the SO lead and relay 2'70 retained operated. Relay 340 closes contacts 343 to place battery on lead SO and therefore ground on S1 to maintain relay 276 as already described and maintain circuits Ztltl and 1% busy in a manner similar to that done on an incoming call from the central ofiice. Thus the operator at the central ofiice may maintain the connection. The manner in which this occurs will be explained more fully in the portion of the specification dealing with incoming calls from the central office. Also the high resistance relay 330 in the loop restores the jack relay to signal the opera Relay 320 is slow-to-release however, and 010- assassin tor in any well known manner so that she may disconnec Relay 3% is then restored to in turn restore relay Relay Edi) removes battery at contacts 343 from lead :30 and relay 2'70 then restores.

Relay releases to restore relay 23d. Relay is already completely restored. Relay 23% opens contacts 2.31 to open the circuit to relay 9%. Simultaneously at contacts it restores the non-operating load for the carrier equipment. Relay 9!) restores to open the holdiog circuit to relay and it in turn opens the circuit to the upper winding of relay fill. Relay restores to place the trunk circuit 1% in condition to be seized by another calling party.

The attendant at the P. A. B. X may initiate a call to an operator at the central office or to a subscriber in the central or nce by plugging her cord circuit in at jack ii after first insuring that the selected trunk circuit is idle by noting that the busy lamp such as 4 individual to the trunl: is dark. inserting her plug in jack l4 opens contacts to remove battery from lead C and closes con tacts 'i to ground lead C so that the trunk circuit is indicated busy to incoming calls from switch train 3. Ground fr n contacts 7 and on lead C is forwarded ove contacts r,., all, the upper winding of slow-tooperate relay St), the tip conductor T and the loop through the operators cord circuit back e e the ring conductor R, contacts 33, the lower left winding of repeating coil @9, to b ry thro= gh the lower winding of relay l Relays and St) operate. Relay it? completes the al'oredescribed circuits to relays 2h, 4: and and they in turn oper te relays 3t St 223- and 316 and complete the afoenientioued holding and loop circuits all in a manner describe The aforedescribed operations take place in the central office termination circuit 3% and at the P. A. X termination circuit ill-l) and automatic switch ing equ pment is associated with the central ofiice termination circuit Ell in the well-known manner, or it the ofiice is a manual one, an operator is signalled, and she responds to the call. in the meantime relay 54) whose energized up er winding originally closed only its X con tacts, completes a circuit from battery through its lower winding to ground through contacts 33 and 32, and is now -lly energized. It completes a loop circuit from ground on one side of may 19, contacts 21 and 31, the loop over the P. A. B. X attendants cord circuit including conductors T and R and contacts 63 to battery through the lower winding of relay 16. At contacts 33 it closes a holding circuit for its lower winding through contacts 323 and its X contacts and also provides an additional ground for lead C, while at contacts 554 it opens the original energizing circuit for its upper winding. At contacts 35 it provides another ground for the busy lamp 4, which already lighted when relay 3t operated.

The dialling and talking circuits are as previously desci .bed on a call from P. A. B. X subscriber S2 with the exception that the just described loop through the attendonts cord circuit and relay 1% is used instead of the and leads and the loop over switch train 3. The attend-ant may dial over the automatic switching equipment to complete the call or have the operator at the called manual oiiice complete the call in accordance with the type of service provided therein.

The attendant at the P. A. B. X disconnecting opens the loop to relay and it releases to open the circuits to relays 2%, t ll, and Relay 7% operates pre viously described to hold relay 5% operated until relay 9t operates on restoration of relay 2t). Relay 7t, restores on restoration of relay Relay 9t now holds relay operated as before described and relay fill holds relay 3i operated.

Relay 21% on releasing causes the release of relay 31% and it in turn causes the operation of relay 350 and the energization of the upper Winding of relay 3%. The central ofiice loop circuit is transferred from relay 376) to relay 33h to cause the release of the automatic V 12 switching equipment or signal the central office operator respectively to disconnect all as previously described. Relay 270 in the P. A. B. X termination circuit 291) is restored as already described. Relay 27h releases relay 2% to in turn release relay 9%. Relay 9% on rel ase now disconnects ground from the upper winding of relay 3:"; by deenergizing relay 5% and it releases to remove ground from the C lead at contacts 32 and from the busy lamp contacts Up to this point the release operation is the ribed on a call by a P. A. B. X subscriber. amp is maintained lighted at contacts and C lead grounded at contacts until relay St releases.

tho

Liv

G93 Relay 3t? on releasing opens the holding circuit to lower winding of relay Ell at contacts 32. and 33, and relay restores to darken the busy lamp and remove ground from the C lead at contacts 35 and respectively so that the trunk circuit tilt) is now available for use.

Incoming calls On a call proceeding from a subscriber in the central office to a subscriber at the l. A. B. X the calling sub-- scriber dials the P. A. B. X number over the automat': switch equipment having access to circuit 3 The 1 st switch in the switch train in the central ofiicc tests for battery in any well-known manner and on finding same extends ground and battery to the :-L and L conductors respectively to operate relay 3% over the previously described prepared loop excepting the ass line circuit line relay. if an operator extending th call to the P. A. B. X she plugs in her cord circuit to extend ground and battery over the +L and -L conductors respectively to operate relay 3%. Relay 333 closes contacts 331 to operate slow-to-release relay 3i turn opens. contacts 348 to disconnect the carrier idle load circuit and closes contacts to place battery the SO lead over contacts 36; to cause the carrier equipment to forward ground over the Si lead to energize the upper winding of relay 276. Relay 279 operates relay which in turn forwards ground through the upper winding of relay 210 from contacts 23i, the upper primary of coil 299, contacts 251 to the T conductor. At contacts 235 it initiates operation of the ringing m""'"ine and 5. contacts 2.0. it disconnects the idle e sui Ground on the +1" conductor is forwarded throi relay 90, over contacts 25', 65 and the "i" conductor. contacts 254 and the lower primary of coil 'z. battery through the lower winding of relay Relay is not energized in series with relay as previously described.

Relay 98 operates and closes contacts 9; to energize relay 58 which in turn prepares its own holding circuit at contacts 53 and extends ground on the +1 conductor through contacts 52 to contacts it. it also closes contacts 54 to energize the upper winding of relay 3% which disconnects battery from the C cone. to tacts At contacts 34 it completes a circ t 1 ing the busy lamp such as 4 at each attencmts posi'ouu calls c-ver switch train 3; forwards ground over contacts 8 and 61, through the upper winding of relay to the +2? conductor and also ground from contacts 32 is lorwarded over contacts 33 to the X springs of relay The connector switch also places interrupted ringing current on the +L and L conductors. The operator does the same by manipulating a ringing lrey at her position. The ringing current is forwarded from the L conductor, A. C. relay 389, condenser 34-9, contacts 351 and back over the +L conductor.

The circuit to relay 3% is opened at contacts 331, but as it is slow-to-release, a holding circuit is completed therefor from contacts 342 and 383 closed by operated relay 380. Relay 380also closes contacts 381 to shunt contacts 361 and closes contacts 332 to operate slow-torelease relay 360. Relay 360 operates to open contacts 361', however battery forwarded over contacts 343 381 remains on the SO lead until relay 380 releases when the A. C. ringing curnut is interrupted. The operating circuit for relay 36d and the holding circuit for relay 34% are temporarily opened at contacts 382 and 383 respectively, however, both hold their contacts operated until relay 3% is reoperated, while relay 330 reoperates to energize relay 3% in the interim. Release of relay 380 causes ground to be removed from the SI lead and the upper winding of relay 27th is deenergized. Although contacts 27ft open relay 23d remains operated as it is slow-to-release and contacts 275 close to energize relay 24th from ground at contacts 2234. release relay 249 closes contacts 2% to prepare its own holding circuit. It also closes contacts 241 and 242 to prepare a circuit for the lower winding of relay 216 and the upper winding of relay 25th respectively.

When the A. C. ringing current is again supplied over contacts 351 and condenser 349 to the A. C. relay 3%, it operates once more to close contacts 331 and forward battery over the S lead to in turn operate relay 270. The holding circuit for relay 3% is again completed and also the operating circuit for relay 36th so that each receives another spurt of energizing current.

Now when relay 27d reoperates it opens the operating circuit for relay 2% at contacts 2'75 and completes the previously prepared holding circuit therefor from contacts 234, 276, 263 and 243. Relay 230 is of course reenergized at contacts 2711. Contacts 274 on closing complete a circuit for the upper winding of relay 250 from ground at contsc c forwarded over contacts 27 242 and 261. Relay Z50 operates to open the first circuit through relays Zllll and 9% at contacts 251 and 253. At contacts 253 resistance battery is supplied to the -T conductor while generator ground is supplied at contacts 252 to the +T conductor by the ringing machine. Contacts 255 include weighted mechanical springs which are arranged to oscillate the contacts in any well-known manner between an open and closed position until contacts 252 and 253 have closed for a predetermined period of time and then maintain contacts 255 in a closed position. Contacts 273 closed by relay 270 provide a short circuit for the upper winding of relay 260 making it slow-to-operate. A circuit is completed from ground at contacts 234, 274 and 242 over contacts 255 to battery through the lower Winding of relay 260 to operate relay 26h. Because of the short circuit on the upper winding of relay 260 it is slow-to-operate, and it does not operate until springs 255 come to rest in their closed position. This provides an operating period of desirable duration for relay 250 so that the signalling current may be supplied for such a desired period of time. Relay 26% opens contacts 261 and closes contacts 262 so that contacts 262 are now in shunt with 255. The shunt is provided around contacts 255 to prevent their burning. The circuit to relay 250 is now open and it restores. At contacts 263 the holding circuit for relay 240 is opened, and its starts to restore. This type of ringing arrangement is unnecessary during daytime periods, as a lamp individual to the trunk is lighted immediately as will be explained, to signal an operator. For night service, however, it is desirable to have the ringing signal applied for a considerable period and therefore this type of arrangement is provided.

The ringing current with ground superimposed thereon, which is applied, while relay 2% is operated, is sent over contacts 252, the +T' conductor through the condenser 98, A. C. relay Q5, thermistor 77, contacts 71, and back over the -T lead to battery through the lower winding of relay 25d. Thermistor 77 is provided for preventing undue surges of current which may occur at various times from afiecting relay @5. Relay 95 operates and closes contacts 96 and 97. Closing contacts 9'7 provides an obvious holding circuit for already operated slow-to-release relay fill Whose operating circuit is opened Slow-towhen relay 9t releases. Relay 6% is operated from battery through its Winding and contacts 96 to ground at contacts 1'35. At contacts or it completes a circuit from ground at contacts 13 and 22 to light the P. A. B. X attendant lamps such as 3 so that an attendant answers the call. At contacts till it opens the prepared circuit to the upper winding of relay Sit and transfers the upper winding to generator ground forwarded over the +T' conductor and contacts 52. At contacts 68 relay 6% prepares a loop circuit for relay lltl. At contacts 63 it disconnects conductors R from the lower left winding coil 9 and connects it directly to the T conductor at contacts 64. At contacts as it disconnects relay 9% from the -T conductor and connects it to resistance battery at contacts 66 to complete another operating circuit for relay from ground on the +1" conductor. At contacts 68 it completes its own holding circuit from contacts 82 and 31, while at contacts 69 it opens a point in the circuit to relay ill. When the night position is used, a cord circuit extends conductors T and R from jack J4 to a ringer at the night position. Ringing current is forwarded over contacts 52, 62, the upper winding of relay so, conductor T, a loop to the night ringeiyconductor R, contacts 64, and the T conductor. The ringer operates to provide an audible signal of desirable length as provided by the duration of time that relay 25d is operated.

As previously stated relay 256 restores, after relay 26% operates, to open contacts 252 and 253 and close contacts 253. and Relay 266 also opens the holding circuit for relay at contacts 263. As relay 244 is slow-to-release it will hold its contacts operated until relay 27h is again released. When relay 2'70 restores after the interruption in another application of ringing current at circuit Elli it opens contacts 274 to restore relay ass. By this time springs 255 are open. Relay 260 releases to prepare relay 25h for operation. Contacts sea, which open when relay 26-8 operates, reclose to prepare the iolding circuit to relay 2%, which is now open at contacts 276. Relay are receives another energizing spurt over its original operating circuit on release of relay 2767. The operating cycle for relays 240, 256 and 2dr) is repeated as often as relay 276 is operated and restored. If only one application of interrupted ringing current is provided relay 246 restores a period of time after relay 26h opened its holding circuit at con tacts 263. The circuit for relay Zoo is opened at contacts 2 52 and it restores. As relay 27% remains operated no further circuits to relay 2% are completed and it remains unoperated. Of course each time the ringing current is disconnected from the +T' and T conductors, relay is restored. Relay oil of course is held operated, While relay 95 is restored, over its previously described holding circuit.

The P. A. B. X attendant on answering completes the circuit from ground on the +T' conductor, contacts 52 and 62, the upper winding of relay 80 over the tip con ductor T and back over ring conductor R, contacts 64 to the T conductor. Nothing occursif relay 250 is operated, however if relay 251i is released the +T and -T conductors are extended to ground and battery respectively through relay 21d. Relay Zltl is operated in this circuit while relay 9% may remain operated over its previously described operating circuit. Relay 80 operates over the above circuit in series with relay 210 to close its X contacts and is now fully energized from ground over contacts 33 and 32, while providing an additional ground for C at contacts 83. At contacts 82 it opens the holding circuit for relay 60, and at contacts as it closes the previously prepared resistance loop for relay in through resistance 2 and contacts 63 before relay to releases. Relay 1o operates to complete an already described loop through relays 4t} and 2th at contacts ill and operates relay 243 at contacts 12. It also darkens the answer lamp by opening contacts l3. Relay 49 operates to complete this previously de scribed holding circuit for relay 5%. Relay 6i} releases contacts 68 to open the circuit for relay 1%, but the already described loop is completed for relay 10 as contacts 21, 81 are closed when contacts 63 close. At contacts 85 an additional ground for the busy lamp is provided. Relay 80 is held operated over the holding circuit to its lower winding when contacts as open while relay 26 opens contacts 25 to restore relay 9% if it is still operated.

Relay 210 on operating closes contacts 212 to cause relay 310 in the central oifice termination circuit to operate as previously described. Relay 22th is operated as previously described to provide an additional holding ground for the upper Winding of relay 2163 at contacts 221. Relay 320 does not operate when relay 3% is now operated as contacts 343. are open. Contacts 313 close to shunt the lower winding of relay 33 3 through contacts 344 and 3 55. This allows a low resist ance relay associated with the loop and in the connector to operate and cut-off the ringing current or if the central office operator is signalling to cause a cord circuit lamp to signal the operator that the P. A. B. X attendant has answered. Likewise in the connector reverse battery answer supervision may now be given.

An already described talking circuit is completed between the P. A. B. X attendant and the calling subscriber in the exchange or the operator in the exchange. The attendant now extends the call through her cord circuit to the desired P. A. B. X subscriber and completes a talking circuit between the calling and called subscriber.

if for any reason the operator at the central ofiice desires to re-ring the attendant she merely manipulates her ringing key to operate and release relay 3%. Relay 3% operates. When relay 3% restores to open contacts 3331 relay 27b is restored in a manner already de scribed to initiate the aforedescribcd cycle of operations for relays 24%, 25-9 and 260. Relay 216 however is held operated by a holding circuit completed over contacts 241, 272 and 222 so that relay 3% in circuit 3% is maintained operated. Signalling current is applied over the +T' and T conductors to operate relay 95 as already described. It in turn rcoperates relay 64 as previously described. Relay 60 opens the circuit to relay ill at contacts 6?; and connects the R conductor to the T conductor at contacts 64. Relay it} releases to open the loop to relays as and 2.19. Relay 21d remains operated over the holding circuit to its lower winding. Relay (it opens the holding circuit for relay 56' but it is SiQ'rV-lG-ICIEQS. Relay 2%} is slow-to-release and remains operated while contacts 12 open and contacts 13 close to light the P. A. B. X attendants lamp over contacts i3, 22 and 67. Relay 6% remains operated only during the period ringing current maintains relay 5E5 operated. it then releases to reoperatc relay it and restore the circuits for relays 2d, 4d, 5d and 21%. The lamp of course is extinguished when contacts 13 open. The cycle may be repeated as often as desired by the operator at the central omce until the attendant answers. At that time the attendant may establish any other desired connection.

Release of the connection by the calling central office subscriber merely causes the automatic switching equipment to restore and places circuit 3% in the same condition as after seizure on an outgoing P. A. B. X call. Likewise the operator at the central oflice on disconnecting places circuit Still in the same condition as after seizure on an outgoing P. A. B. )1 call. Release of the connection by the P. A. B. X attendant causes the restoration or" all the operated relays in circuit 1%, and 31% all as previously described and places these circuits in condition to be seized for another call.

Thus having described my invention and its manner or" operati n, but believing it capable of more widespread tlilli afon and novelty than the particular embodiment described herein 1 wish to claim the subject matter incorporated in the accompanying claims.

, What is claimed is:

l. in a communication system of the class including a private exchange and a central oflice to which said private exchange is connected by means of a carrier circuit over which a call may be completed from said central oflice to said private exchange and from said private exchange to said central oflice and wherein said central olfice and said private exchange each have a loop circuit for transmitting signals to and from said carrier circuit, each loop circuit normally only partially completed to battery through a relay and wherein means at said central oificc are provided to enable a subscriber in said central orfice to complete the central office loop circuit and energize the associated relay on a call to said private exchange, the improvement comprising means at said central ofiice operated in response to the energization of said relay thereat for controlling said carrier circuit to transmit a signal to said private exchange, and means at said private exchange operated in response to the transmission of said signal to said private exchange for preventing completion of the loop circuit and energization of the relay at said private exchange to thereby prevent a call from said private exchange to said central office.

2. A system such as claimed in claim 1 in which said means for completing said central office loop circuit includes an arrangement for applying ringing current to said loop circuit, means associated with said central office loop circuit operated on the application of ringing current thereto, said last operated means controlling said carrier circuit accordingly to transmit appropriate signals to said private exchange, and means in said private exchange operated in response to the transmission of said appro priate signals for providing ringing current at said private exchange to signal said private exchange accordingly and enable the completion of the loop circuit and energization of the relay thereat.

3. in a system such as claimed in claim 2, means at said private exchange operated on answer by the attendant thcreat for completing the loop circuit at said private exchange and energizing the relay thereat, said energized relay controlling said carrier circuit to transmit a corre- 'sponding signal, and means at said central oilice operated thereby for signalling said central oflice subscriber that the attendant at said private exchange has answered.

4. In a communication system of the type having a private exchange and a central office and including carrier equipment therebetween for efiectuating a communication circuit from said private exchange to said central oflice and from said central ollice to said private exchange, a first circuit in said private exchange and another circuit in said central office said first circuit signalling said private exchange on a call thereto from said central office and said other circuit signalling said central oilice on a call thereto from said private exchange, each signalling circuit normally connected to battery through a signal relay Which is energized by connecting said circuit to ground to thereby provide a signal, the improvement comprising a relay associated with each signalling circuit and operated in response to a signal transmitted over said carrier equipment, means operated on an outgoing call from said private exchange to said central office for causing said carrier equipment to transmit a signal for operating the relay in the central ofiice, said operated relay connecting its associated signalling circuit to ground to thereby operate the signal relay in said circuit for signalling said central office, and means operated on an outgoing call from said central otlice to said private exchange for causing said carrier equipment to transmit a signal for operating the relay in the private ofiice for connecting ground to its associated signalling circuit to thereby operate the signal relay said'circuit to signal the private exchange.

5. For use in establishing a communication circuit between one exchange including an attendants position and switching equipment whereby a subscriber at a station therein may extend a connection to a first two conductor line arranged in an incomplete circuit with battery connected through a relay to one of the conductors and from said two conductor line to carrier equipment provided for extending a communication circuit from said first two conductor line to a second exchange wherein a second two conductor line is provided, said second two conductor line arranged in an incomplete circuit with one conductor connected to battery through a relay and wherein said second exchange includes switching equipment whereby a connection and a communication circuit may be extended from said second two conductor line to a station in said second exchange, the improvement comprising means re, sponsive to a station in said one exchange being connected by the associated switching equipment to said first two conductor line for completing a circuit including both conductors thereof and the associated relay for operating said relay, means operated by said operated relay for controlling said carrier equipment, means in said second exchange operated by said controlled carrier equipment for completing a circuit including both conductors of the second line and the associated relay for operating said associated relay to thereby cause the switching equipment in said second exchange to be associated with said second two conductor line and whereby said second line is arranged to form ailoop circuit for controlling said second exchange switching equipment, said means for operating said relay in said second exchange thereafter responsive to signalling pulses transmitted over said first switching equipment from said one station and repeated by said relay in said first exchange for controlling said carrier equipment accordingly to thereby control the loop circuit in said second exchange to operate the switching equipment in said second exchange to establish a connection to a called subscriber whereby a communication circuit including said first and second two conductor. lines and said carrier equipment is established on answer by a subscriber at a called station. t

, 6. For use in establishing a communication circuit between one exchange including an attendants position and switching equipment whereby a subscriber at a station therein may extend a connection to a first two conductor line arranged in an incomplete circuit with battery connected through a relay to one of the conductors and from said two conductor line to carrier equipment provided for extending a communication circuit from said first two conductor line to a second exchange wherein a second two conductor line is provided, said second two conductor line arranged in an incomplete circuit with one conductor connected to battery through a relay and wherein said second exchange includes switching equipment whereby a connection and a communication circuit may be extended from said second two conductor line to a subscriber in said second exchange, said second exchange switching equipment available to a subscriber at a station in said second exchange for establishing a connection and a communication circuit from said last subscriber to said operated relay for controlling said carrier equipment,

means in said second exchange operated by said controlled carrier equipment for completing a circuit with the second two conductor line to operate its associated relay to thereby cause the switching equipment in said 'second exchange to be associated with said second two conductor line and whereby said second line is arranged controlling said carrier equipment, means in said one exto form a loop circuit for controlling said second exchange switching equipment, said means for operating said relay in said second exchange thereafter responsive to signalling pulses transmitted over said first switching equipment and repeated by said relay in said first exchange for controlling said carrier equipment and the second exchange switching equipment over said second two conductor line ,to establish a connection and a communication circuit to a called subscriber, said second exchange switching equipmenteffective on a call from a subscriber in said second exchange to said one exchange to complete a circuit with said two conductors of said second line, means thereafter controlled by said second two conductor line for controlling said carrier equipment, means in said one exchange controlled by said controlled carrier equipment for completing a circuit with said two conductor line in said one exchange, means operated when said last circuitis completed for preventing the relay in said one exchange from operating, means in said second exchange controlled by the, application of signalling current to said two conductor line in. said second exchange for controlling said carrier equipment to, there'- by control said controlled means in said one exchange, and means operated when said last controlled means is controlled in response to the application of said signalling current for signalling said attendants position.

7. For use in establishing a communication circuit between one exchange including an attendants position and switching equipment whereby a subscriber at a station therein may extend a connection to a first two conductor conductor line to a secondexchange wherein a second two conductor line is provided, said second-two conductor line arranged in an incomplete circuit withone conductor connected to battery through a relay, and wherein said second exchange includes switching equipment whereby a connection and a communication circuit may be extended from said second two conductor line to a subscriber at a station in said second exchange, said second exchange switching equipment available to a subscriber in said second exchange for establishing a connection and a communication circuit from the associated station to said second two conductor line, said last switching equipment including means for applying signalling current to said two conductor line when a connection thereto is established from a station in said second exchange, the improvement comprising means responsive to a statio n in said one exchange being connected by the associated switching equipment to said first two conductor line for completing a circuit therewith to operate said relay connected to said one conductor, means operated by said operated relay for controlling said carrier equipment, means in said second exchange operated by said controlled carrier equipment for completing a circuit including said two conductor second line to operate said associated relay to thereby cause the switching equipment in said second exchange to be associated with said second jtwo conductor line and whereby said second two conductor line is arranged to form a loop circuit for controlling-said second exchange switching equipment, said 'rneansforoperating said relay in said second exchange thereafter responsive to signalling pulses transmitted over said first switching equipment by said first subscriber and repeated by said relay in said first exchange to control change controlled by said Controlled carrier equipment for completing a circuit with .said two conductor line in said one. exchange, means thereafter operated for preventing the relay in .said' one exchange from operating, means in said second exchange controlled by the application of signalling current to said two conductor line in said second exchange for controlling said carrier equipment to thereby control said controlled means in said one exchange accordingly, means operated when said last controlled means is controlled in response to the application of said signalling current for signalling said attendants position, and means operated on answer by the attendant at said position for operating said relay at said one exchange over said first two conductor line at said exchange to establish a communication circuit between said calling subscriber and the attendant including said first and second two conductor lines and said carrier equipment.

8. In a communication system of the class having a private exchange with private lines, switching equipment and an attendants position, said private exchange connected to a central ofi'ice overa connection including carrier equipment, said private exchange having a terminating connection in said central oflice comprising two conductors, one of said conductors having battery connected thereto through two control relays, said central oflice including switching equipment available to said private exchange for completing a connection to a station in said central ofiice and available to a subscriber at a station in said central ofiice for enabling the completion of a connection to said two conductors and adapted to provide signalling current over said conductors on completion of a connection thereto, the improvement comprising a first circuit in said private exchange completed by a subscriber at one of said private lines on initiating a call to a subscriber in said central office and dialling a predetermined digit on the private exchange switching equipment, said first circuit thereafter arranged to control said carrier equipment and to transmit dial impulses received from said private line over said carrier equipment to said central office, a control circuit ineluding a third relay at said central oflice, means at said central oifice operated in response to the control of said carrier equipment for disconnecting one of said control relays from said one conductor and for completing said control circuit over said one conductor and the other control relay to thereby operate said other control relay and the third relay of said control circuit, said other control relay operated for associating the central ofiice switching equipment with both said conductors, means operated by said third relay for enabling the control of said central ofiice switching equipment over said two conductors, said means operated in response to the control of said carrier equipment also operated in accordance with dial impulses received by said first circuit inrsaid private exchange and transmitted over said carrier equipment to control said means accordingly, means operated by said controlled means in said central oflice in accordance with said dialled digits for operating said central office switching equipment over said two conductors to establish a connection to a station in said central ofiice, said central ofiice switching equipment operated on a call initiated by a subscriber in said central ofiice to said private exchange for establishing a loop circuit including said two conductors and said two control relays whereby only the one control relay is operated, means operated by said operated one control relay for controlling said carrier equipment, means in said private exchange operated in response to said last control for preventing the completion of said first circuit in said private exchange, means at said central oflice operated in response to the provision of signalling current over said two conductors for controlling said carrier equipment accordingly, signalling means in said private exchange, said signalling means in said private exchange operated in response to the control of said carrier equipment by said signalling current operated means forsignallin'grsaid attendants position, and means operated on answer by the attendant at said position for completing said first circuit to thereby establish a talking circuit to the calling subscriber including said first circuit, carrier equipment and two conductors.

9. In a communication system of the class having a private exchange with private lines, switching equipment and an attendants position, said private exchange connected to a central oflice over a connection including carrier equipment, said private exchange having a terminating connection in said central office comprising two conductors, one of said conductors having battery connected thereto through two control relays, said central office including switching equipment available to said private exchange for completing a call to a subscriber in said central office and available to a subscriber at a station in said central ofiice for enabling the completion of a connection from the station to said two conductors and adapted to provide signalling current over said conductors on completion of a connection thereto, the improvement comprising a first circuit in said private exchange completed by a subscriber at one of said private lines on initiating a call to a subscriber in said central ofiice and dialling a predetermined digit on the private exchange switching equipment, said first circuit thereafter arranged to control said carrier equipment and to transmit dial impulses received from said private line over said carrier equipment to said central ofiice, a control circuit including a third relay at said central oflice, means at said central office operated in response to the control of said carrier equipment for disconnecting one of said two control relays from said one conductor and for completing said control circuit through said third relay and over said one conductor and the other control relay to thereby operate said other control relay and the third relay, said other control relay operated for associating the central office switching equipment with both said conductors, means operated by said included relay for enabling the control of said central ofiice switching equipment over said two conductors, said means operated in response to the control of said carrier equipment also operated in accordance with dial impulses received by said first circuit in said private exchange and transmitted over said carrier equipment, means operated by said control means in said central oifice in accordance with said dialled digits for operating said central office switching equipment over said two conductors to establish a connection to a subscriber in said central ofiice, said central ofiice switching equipment operated on a call initiated by a subscriber in said central oflice to said private exchange .for establishing a loop circuit including said two conductors and said two control relays whereby only said one control relay is operated, means operated by said operated one control relay for enabling the control of said carrier in response to the provision of signalling current thereto, means at said central office operated in response to the provision of signalling current over said two conductors for controlling said carrier equipment accordingly, and signalling means in said private exchange, said signalling means in said private exchange operated in response to the control of said carrier equipment by said signalling current operated means for signalling said attendants position.

10. In a communication system of the class having a private exchange with private lines and switching equipment, said private exchange connected to a central office over a connection including carrier equipment, said private exchange having a terminating connection in said central office comprising two conductors, one of said conductors having battery connected thereon through a relay, said central oflice including switching equipment available to said private exchange for completing a connection to a subscriber in said central oifice, the imfice and dialling a predetermined digit on the private exchange switching equipment, said first circuit thereafteraranged to control said carrier equipment to transmit dial impulses received ,from said private line over said carrier equipment to said central ofiice, a control circuit including a relay at said central office, means at said central office operated in response to the control of said carrier equipment for completing said control circuit over said one conductor and its connected relay to battery to thereby operate both relays, said connected relay operated for connecting the central ofiice switching equipment with both said conductors, means operated by said included relay for enabling the control of said central office switching equipment over said two conductors, said means operated in response to and in accordance with dial impulses transmitted by said carrier equipment when crating said central office switching equipment over said two conductors to establish a connection to a subscriber in said central oflice.

11. -In a communication system including a private exchange and a central office to which said private exchange is connected by means of a carrier circuit and wherein a loop circuit corresponding to said private exchange is partially completed to battery through a first relay, connecting means at said central oflice for completing a connection from said loop circuit to a station in said central oflice, said connecting means also effective on a call initiated by a subscriber 'at a station in said central ofiice to complete a connection from the station to said loop circuit, the improvement comprising a second relay at said central ofiice operated over said carrier circuit on a call from said private exchange to said central office for disconnecting said first relay from said loop circuit and for completing said loop circuit to prevent said connecting means from completing a connection thereto on a call from a subscriber in said central office and tor establishing control of said connecting means via said loop circuit, controlled means thereafter controlled over said carrier circuit for causing said connecting means to be operated -via said loop circuit for establishing a connection to a subscriber in said central ofiice, and means including a portion of said first loop circuit effective in case of -'a connection established to said loop circuit by said connecting means on a call from a subscriber in said central oflice for operating said disconnected second relay to cause said carrier circuit to signal said private exchange.

12. For use in establishing a communication circuit between one exchange including an attendants position and switching equipment whereby a subscriber at a station therein may extend a connection to a two conductor line arranged with battery connected through a relay to one of 'the conductors and with the other conductor normally unconnected to a source of potential and from said two conductor line to carrier equipment provided for extending a communication circuit from said first two conductor line to a second exchange wherein a second two conductor line is provided, said second two conductor line arranged so that one conductor is connected to battery through a relay and the other conductor is normally unconnected to a source of potential and wherein said second exchange includes switching equipment whereby a connection and a communication circuit may be extended from said second two conductor line to a station in said second exchange, said second exchange switching equipment available to a subscriber at a station in said second exchange for establishing a connection and a communication circuit from said last station to said second two conductor line, said last switching equipment ineluding means for applyinglsignalling current to said two conductor line'when a connection thereto is established from a station in said second exchange, the improvement comprising means responsive to a station in said one exchange being connected to said first 'two conductor line for closing the unconnected conductor thereof to a source of potential for operating said relay connected to ond line to form a loop circuit for controlling said second exchange switching equipment, said means for operating said relay in said second exchange thereafter responsive to signalling pulses transmitted over said first switching equipment from said station in said first exchange and by said relay in said first exchange over said carrier equipment for controlling the second exchange switching equipment over said second two conductor line to establish a connection to a called station therein where by -'a communication circuit is established between said called station and said calling station, said second exchange switching equipment efiective on a call from a subscriber at a station in said second exchange to said one exchange to connect said unconnected conductor of said second line to a source of potential, means thereafter controlled by said second two conductor line for controlling said carrier equipment, means in said one exchange controlled by said controlled carrier equipment for connecting the unconnected conductor in said one exchange to a source of potential, means operated when said unconnected conductor is connected to said source of potential for preventing the relay in said one exchange from operating, and means in said second exchange controlled by the application of signalling current to said two conductor line in said second exchange for controlling said carrier equipment to thereby control said controlled means in said one exchange accordingly, means operated when said last controlled means is controlled in response to the application of said signalling current for signalling said attendants position, and means operated on answer by the attendant at said position for operating said relay at said one exchange over said two conductor line at said exchange, said means operated by said relay operated for controlling said carrier equipment to control the means in said second exchange controlled by said controlled carrier equipment for preventing the application of signalling current to the two conductor line in said second exchange.

l3. In a communication system of the class having a private exchange with private lines, switching equipment and an attendants position, said private exchange connected to a central office over a connection including carrier equipment, said private exchange having a terminating connection in said central office comprising two conductors, one of said conductors having battery connected thereon through two relays, said central oifice including switching equipment available to said private exchange for completing a connection to a subscriber in said central ofiice and available to a subscriber in said central oflice for enabling the completion of a connection to said two conductors and adapted to provide signalling current over said conductors on completion of a connection thereto, the improvement comprising a first circuit in said private exchange completed by a subscriber at one of said private lines on initiating a call to a subscriber in said central ofiice and dialling a predetermined digit on the private exchange switching equipment, means operated by said completed circuit for controlling said carrier equipment, a control circuit including a relay at said central ofiice,

6 :23 means at said central office operated in responseto the control of 'said carrier equipment for disconnecting one of .said two relays from its conductor and for completing said control circuit through'its included'relayover said one conductor and' the other relay to battery to thereby operate'said otherrelay and the included relay, said other relay operated for connecting the central office switching equipment with both said conductors, means operated by :said included relay for enabling the control of said central ing equipment over said two conductors to establish a connection to a subscriber in said central oifice, said cen 'tral oifice switching equipment operated on a call initiated by a subscriber in said central office to said private exchange for establishing a loop circuit including said two conductors and said two relays connected to said one conductor whereby only said formely disconnected relay is operated, means operated by said operated formerly r 1 disconnected relay :for controllingsaid carrier equipment, -means= at said private exchange operated'in response to the last-control; of said carrier equipment for preventing the completion of said first circuit in said private exchange, means at said central office operated in response to the provision of signalling current over said two conductors for'controlling said carrier equipment, signalling means in said private exchange, said signalling means in said private exchange operated in response to the control of said carrier equipment by said signalling current operated means for'signalling said attendants position, and

means operated on answer by the attendant at said posi tion for completing said first circuit in said private exchange, said completed'first circuit controlling said carrier equipment for operating said first means operated thercbyin said central office for preventing the provision of further signalling current to said two conductors by said central ofiice' switching equipment.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,836 Almquist et al June 25, 1935 

